We use this at work and it's awesome. Solved a lot of big problems and a lot of little problems, like "works on my machine but not prod" and rebuilding your dev env when you switch machines. etc.
The one thing that became a problem was managing vmware (the plugin is a closed source one, so it was hard to debug any issue that came up with it - easily solved by writing our own open source one)
I'm guessing that it either uses absorption spectrography or a motor, two electrodes, a balance, and a large database of mass/conductivity/viscosity data.